Controlling the cutting to hydration ratio in the refining of pulp

ABSTRACT

The quality of paper being manufactured is maintained constant by keeping the cutting to hydration ratio of pulp stock during refining constant. The drying rate of the paper is an indication of the cutting to hydration ratio of the refined pulp stock. The drying rate is compared with a desire drying rate and the difference therebetween is used to adjust the refining so that the actual cutting to hydration ratio is maintained the same as the desired cutting to hydration ratio.

Unite States Patent Inventors Charles R. Bietry;

Earl D. Hogan, both of Rochester, N.Y. Appl. No. 863,618 Filed Oct. 3,1969 Patented Dec. 28, 1971 Assignee Eastman Kodak Company Rochester,N.Y.

CONTROLLING THE CUTTING TO HYDRATION RATIO IN THE REFINING OF PULP 8Claims, 2 Drawing Figs.

US. Cl 162/198, 162/254, 162/263, 241/37 Int. Cl. D2ld 1/20 Field ofSearch 162/ 198,

PULP

[56] References Cited UNITED STATES PATENTS 2,699,095 1/1955 Irwin241/37 X 3,196,072 7/1965 Wirtz 162/263 X 3,490,689 1/1970 Han et a1162/252 X Primary Examiner-S. Leon Bashore Assistant Examiner-Alfred D.Andrea, Jr. Attorneys-Walter O. I-Iodsdon and Robert F. Cody ABSTRACT:The quality of paper being manufactured is maintained constant bykeeping the cutting to hydration ratio of pulp stock during refiningconstant. The drying rate of the paper is an indication of the cuttingto hydration ratio of the refined pulp stock. The drying rate iscompared with a desire drying rate and the difference therebetween isused to adjust the refining so that the actual cutting to hydrationratio is maintained the same as the desired cutting to hydration ratio.

g COMPU rEfi PATENTED 0mm CHARLES R. B/ETRY EARL D. HOGAN INVENTORSATTORNEYS CONTROLLING THE CUTTING TO I'IYDRATION RATIO IN THE REFININGOF PULP BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates in general to the manufacture of paper; and inparticular to apparatus and methods for controlling the quality ofpaper.

2. Description Relative to the Prior Art Depending on the refining ofpaper pulp, cutting" an hydration are produced in varying amounts. Thecutting relates to the severing of pulp fibers (formation); and thehydration relates to the mashing of pulp fibers (strength). Hydration isnot water content.

It is the present practice to remove periodically a sample strip frompaper being manufactured, thereby to perform various checks to determinethe characteristics of such paper. It is, as a result of such checks,usual to find that paper strength has gradually increased at the expenseof gradually decreasing paper formation, thus evidencing that the pulprefiner has gradually dulled. A technician will then adjust the pulprefiner to increase its ability to cut," thereby to maintain the paperformation at, or close to, a predetermined set point.

Aside from consuming valuable technician time, the prior art method ofcontrolling paper formation (vis-a-vis paper strength) is lacking intight control, i.e., considerable lowquality paper may be manufacturedbefore and during the time when the technician is performing his checks.

The best known prior art may be found in U. S. Pat. Nos. 3,260,642,2,951,007, 2,942,352, 2,922,475, 1,971,296 and 3,073,153.

SUMMARY OF THE INVENTION The invention permits the preselection andmaintenance of a given quality for paper being manufactured. To thisend, the invention employs a computer that effectively calculates thecutting to hydration ratio (C/I-I) of refined pulp, i.e., stock, used inpaper manufacturing, thereby to control paper formation (with respect topaper strength). It has been found that the rate at which stock driesinto paper during paper manufacture is a reflection of its hydration:the greater the hydration, the lower the rate at which such stock dries,and vice versa. Thus, for a given stock (and drying temperature) thedrying rate thereof will vary directly with the cutting thereof, andinversely with the hydration thereof. By equating the actual drying rate(d) for a given stock with a preselected drying rate (11,) for thatstock (which preselected drying rate-at a given drying temperatureiscompatible with paper of a certain desired formation, the errortherebetween may be used to controleither manually or automaticallytheadjustment of the pulp refiner, thereby to maintain the desired paperformation. As presently preferred, the drying rate for stock isdetermined from the moisture content of such stock before and after suchstock respectively enters and exits from a paper drying stage. (Suchdrying stage, however, should not be one wherefrom bone dry" paperexits, this being because no moisture is removed from such paper forpart of its passage through such drier; and so, the entering and exitingmoisture measurements would lead to a false indication of the dryingrate.) As intimated above, the drying rate for stock is dependent notonly on the cutting to hydration ratio, but is also directly dependenton the drying temperature, i.e., d S(C/H), where S is some temperaturedependent variable such as the pressure of steam within the dryingstage. Thus, the cutting to hydration ratio is more properly reflectedin terms of stock drying rate per units of temperature (d/s); and in thepresently preferred form of the invention, the instantaneous d/s isequated with a reference Zi,sl,for quality control purposes.

An object of the invention is to provide improved apparatus and methodsfor manufacturing paper.

Another object of the invention is to provide apparatus and methods forcontrolling the quality of paper during manufacture thereof.

Another object of the invention is to detect, and correct for,inefficient operation of a pulp refiner.

Another object of the invention is to provide control of a pulp refinerin accordance with the cutting to hydration ratio of pulp stockprocessed thereby.

Another object of the invention is to provide a way to determine thecutting to hydration ratio for pulp stock from its drying rate.

The invention will be described with reference to the figures, whereinFIG. 1 is a diagram useful in describing the invention, and

FIG. 2 is a block diagram illustrating a presently preferred form of theinvention.

Referring to FIG. 1, a family of three curves illustrates therelationships among stock drying rate (ii); drying temperature (S), andpaper formation (C/I-I). For a given drying temperature (S and a givendesired paper formation ((C/H)2), the drying rate for stock should be21,. Thus, in the event that the drying rate decreased to a leveli1,,there being no drying temperature changea decrease in paperformation, to one having a cutting to hydration ratio ((C/I-I)3), isevidenced. The present invention, as indicated below in connection withFIG. 2, employs such drying rate differences to control paper formation.

Referring then to FIG. 2, raw pulp is passed through a refiner 10 such,for example as a jordan. The refiner I0, typically, has parts 12 and 14,which are relatively rotatable about a common axis by means of a motor16.

The stock output of the refiner is, in conventional manner, passedthrough a paper-forming fourdrinier 18, after which such stock is dried(22,24) into a bone dry paper web, calendered (26), and rolled (28). Thedriers 22, 24 are steam (30) operated; and the stock drying rate, aspresently preferred, is determined as follows:

A first beta gauge 32, for producing a signal (MA) representing thestock moisture content per unit of web area, is situated at the entranceof the driver 22; and a second beta gauge 34, for producing a signal(M'IA) representing the stock moisture per unit of web area is situatedat the exit of the drier 22. The moisture levels (MIA) and (M'IA) arecompared (subtraction device 38) to produce a loss in moisture signal(MM/A), which when multiplied (40) by the web speed (tachometer 42) andweb width (selector 44) produces a signal (3,) representing the actualrate at which the stock dries into paper.

Since steam pressure is analogous with the drying temperature of thedriers (22,24), it is used to drive, via a diaphragm actuator 46, thewiper 48 of a pickoff potentiometer 50, thereby to product a signal(S,,) representative of the actual temperature of the driers 22,24. Adivider 52 is provided to produce the quotient signal (fl /S which isdirectly related to the cutting to hydration ratio (C/I'I) for the paperbeing manufactured. See the equations of FIG. 1. A comparator 54 equatesthe signal (Zi /S with a preselected fonnation signal (2i,/S,selector56-the error therebetween being applied to control the operation of amotor 58. The motor 58 relatively positions axially the parts 12,4 ofthe refiner 10, thereby to close (or open) the bite of the refiner. Anerror signal produced by the comparator 54 evidences a dulling of therefiner parts 12,14, and which dulling would be reflected in a degradedproduct formation were it not for the fact that, in accordance with theinvention, the bite of the refiner I0 is taken up to cancel such errorsignal, thereby to maintain product formation.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. Below is a list of some of the modifications which are withinthe purview of the invention:

a. Whereas beta gauges are employed for determining drying rates, theuse of other drying rate measurement devices is possible.

b. Whereas the cutting to hydration ratio is calculated, the hydrationto cutting rate could just as easily have been calculated, the operationof the motor 58 being reversed accordingly.

. Whereas paper formation is indicated as being controlled in relationto paper strength, the reverse is a possibility.

d. Where as analogue computation is indicated, digital comdrying ratefor said stock,

b. means providing a drying rate reference signal, and

c. means producing a signal dependent on the difference between saidsignal that varies directly with said drying rate and said referencesignal, said difference dependent signal being said control signal.

4. The apparatus of claim 3 wherein said system includes a plurality ofstock drying means, and said means for producing a signal that variesdirectly with said drying rate produces a signal that varies directlywith the drying rate for said stock at at least one of said stock dryingmeans which precedes that drying means where said stock becomes dry.

5. The system of claim 3 wherein said signal that varies directly withsaid drying rate is a signal that varies as a direct function of therate of drying for said stock and as an inverse function of the stockdrying temperature.

6. The system of claim 4 wherein said signal that varies directly withsaid drying rate is a signal that varies as a direct function of therate of drying for said stock and as an inverse function of the stockdrying temperature.

putation may be employed instead. Various analogue elements forimplementing the computation may be found in ELECTRONIC ANALOGUECOMPUTERS, Korn and I0 Korn, McGraw-Hill Book Company, Inc., N.Y.Whereas closed loop control of the refiner is indicated, the signaloutput from the comparator 54 may instead have been applied to ameterrather than to the motor 58-thereby to control manually the refinersetting IS without the indicated prior art need for paper tests. f. Alead device may be employed between the comparator 54 and motor 58 tocompensate for the delay (fourdrinier 18, drier 22) between the time therefiner first starts to produce stock with a low cutting to hydrationratio and the time such cutting to hydration ratio is computed; orapplication of the signal output from the comparator 54 may be appliedto adjust the bite of the refiner in discrete increments, etc.

What is claimed is:

1. In a paper making system of the type having adjustable means forregulating the cutting to hydration ratio of pulp stock, the improvementcomprising:

a. means for producing a control signal proportional to the differencebetween a preselected cutting to hydration ratio and the actual cuttingto hydration ratio of the said pulp stock, and

b. means responsive to said signal for use in setting the saidadjustable means to maintain the actual cutting to hydration ratio thesame as the said preselected cutting to hydration ratio.

2. The system of claim 1 wherein:

a. said adjustable means is a pulp refiner, and

b. said signal is applied to adjust said pulp refiner in proportionthereto.

3. The system of claim 1 wherein said signal producing means includes:

a. means for producing a signal that varies directly with the 7. Incombination with a paper making machine having a jordan, a paper formingmeans, and stock drying means,

a. means for producing a signal that varies directly with the rate atwhich said stock is dried by said drying means,

b. means providing a drying rate reference signal,

c. means for comparing said reference signal and said signal that variesdirectly with said drying rate to produce a control error signal, and

d. means for use in adjusting said jordan in proportion to the magnitudeof the said control error signal. 8. The method of controlling paperquality comprising the steps of

2. The system of claim 1 wherein: a. said adjustable means is a pulprefiner, and b. said signal is applied to adjust said pulp refiner inproportion thereto.
 3. The system of claim 1 wherein said signalproducing means includes: a. means for producing a signal that variesdirectly with the drying rate for said stock, b. means providing adrying rate reference signal, and c. means producing a signal dependenton the difference between said signal that varies directly with saiddrying rate and said reference signal, said difference dependent signalbeing said control signal.
 4. The apparatus of claim 3 wherein saidsystem includes a plurality of stock drying means, and said means forproducing a signal that varies directly with said drying rAte produces asignal that varies directly with the drying rate for said stock at atleast one of said stock drying means which precedes that drying meanswhere said stock becomes dry.
 5. The system of claim 3 wherein saidsignal that varies directly with said drying rate is a signal thatvaries as a direct function of the rate of drying for said stock and asan inverse function of the stock drying temperature.
 6. The system ofclaim 4 wherein said signal that varies directly with said drying rateis a signal that varies as a direct function of the rate of drying forsaid stock and as an inverse function of the stock drying temperature.7. In combination with a paper making machine having a jordan, a paperforming means, and stock drying means, a. means for producing a signalthat varies directly with the rate at which said stock is dried by saiddrying means, b. means providing a drying rate reference signal, c.means for comparing said reference signal and said signal that variesdirectly with said drying rate to produce a control error signal, and d.means for use in adjusting said jordan in proportion to the magnitude ofthe said control error signal.
 8. The method of controlling paperquality comprising the steps of a. refining pulp into stock, b. feedingsaid refined stock through a paper forming means, c. drying said stockto form paper, d. determining the drying rate for said stock relative toa desired drying rate that is compatible with a certain quality paper,and e. regulating the refining of said pulp so that the actual dryingrate for said stock is the same as said desired drying rate.